Metadata based hypermedia management system

ABSTRACT

A system supplies links between objects. A link service receives a hypermedia link request from a client. The hypermedia request identifies a source object. A link provider analyzes association metadata and creates hypermedia links between the source object and associated objects identified from the metadata.

BACKGROUND OF THE INVENTION

The present invention relates to hypermedia links. More specifically,the present invention relates to managing hypermedia links betweenobjects.

A number of different databases will first be discussed, although itwill be appreciated that the objects need not reside in a database atall. In conventional relational databases, that can be used to store theobjects, all data are stored in named tables. The tables are describedby their features. In other words, the rows of each table contain itemsof identical type, and the definitions of the columns of the table(i.e., the column names and the data types stored in the column)describe the attributes of each of the instances of the object. Byidentifying its name, its column names and the data types of the columncontents, a table is completely described. Queries to a relational database are formulated in a query language. One such language is SQL(Structure Query Language) which is widely used in commercial relationaldata base systems. The data types offered by SQL can be classified ascharacter arrays (names), numbers, and data types related to date andtime. Tables can be modified or combined by several operations ofrelational algebra such as the application of Boolean operators,projection (i.e. selection of columns) or the Cartesian product.

Relational databases offer several advantages. Database queries arebased on a comparison of the table contents. Thus, no pointers arerequired in relational databases, and all relations are treateduniformly. Further, the tables are independent (they are not related bypointers), so it is easier to maintain dynamic data sets. The tables areeasily expandable by simply adding new columns. Also, it is relativelyeasy to create user-specific views from relational databases.

There are, however, a number of disadvantages associated with relationaldatabases as well. For example, access to data by reference toproperties is not optimal in the classical relational data model. Thiscan make such databases cumbersome in many applications.

Another recent technology for database systems is referred to as objectoriented data base systems. These systems offer more complex data typesin order to overcome the restrictions of conventional relationaldatabases. In the context of object oriented data base models, an“object” includes both data and the methods which can be applied to theobject. Each object is a concrete instance of an object class definingthe attributes and methods of all its instances. Each instance has itsunique identifier by which it can be referred to in the database.

Object oriented databases operate under a number of principles. One suchprinciple is referred to as inheritance. Inheritance means that newobject classes can be derived from another class. The new classesinherit the attributes and methods of the other class (the super-class)and offer additional attributes and operations. An instance of thederived class is also an instance of the super-class. Therefore, therelation between a derived class and its super-class is referred to asthe “isA” relation.

A second principle related to object oriented databases is referred toas “aggregation.” Aggregation means that composite objects may beconstructed as consisting of a set of elementary objects. A “containerobject” can communicate with the objects contained therein by theirmethods of the contained objects. The relation between the containerobject and its components is called a “partOf” relation because acomponent is a part of the container object.

Yet another principle related to object oriented databases is referredto as encapsulation. According to encapsulation, an application can onlycommunicate with an object through messages. The operations provided byan object define the set of messages which can be understood by theobject. No other operations can be applied to the object.

Another principle related to object oriented databases is referred to aspolymorphism. Polymorphism means that derived classes may re-definemethods of their super-classes.

Objects present a variety of advantages. For example, operations are animportant part of objects. Because the implementations of the operationsare hidden to an application, objects can be more easily used byapplication programs. Further, an object class can be provided as anabstract description for a wide variety of actual objects, and newclasses can be derived from the base class. Thus, if an applicationknows the abstract description and using only the methods provided by,the application can still accommodate objects of the derived classes,because the objects in the derived classes inherit these methods.However, object oriented data bases are not yet as widely used incommercial products as relational data bases.

Yet another database technology attempts to combine the advantages ofthe wide acceptance of relational data bases and the benefits of theobject oriented paradigm. This technology is referred to asobject-relational database systems. These databases employ a data modelthat attempts to add object oriented characteristics to tables. Allpersistent (database) information is still in tables, but some of thetabular entries can have richer data structure. These data structuresare referred to as abstract data types (ADTs). An ADT is a data typethat is constructed by combining basic alphanumeric data types. Thesupport for abstract data types presents certain advantages. Forexample, the operations and methods associated with the new data typecan be used to index, store, and retrieve records based on the contentof the new data type.

Some conventional object-relational databases support an extended formof SQL, sometimes referred to as ObjectSQL. The extensions are providedto support the object model (e.g., queries involving object attributes).However, these object-relational databases are still relational becausethe data is stored in tables of rows and columns, and SQL, with someextensions, is the language for data definition, manipulation, andquery. Both the target of a query and the result of a query are stilltables. The extended SQL language is often still the primary interfaceto the database. Therefore, there is no direct support of host objectlanguages and their objects. This forces programmers to continue totranslate between objects and tables.

Thus, in prior object-relational databases, an object can be queried forin terms of the objects fields, rather than using the relationaldatabase column names.

However, a number of problems exist with respect to conventional userinterface (UI) technology for object-relational databases and otherdatabases or environments (other than databases) where links betweenobjects are desired.

Conventional user interfaces are hand written. This includes the linksbetween different pieces of data in the databases. Each time such a linkis desired, it must be hand written again. For example, if an orderentry page has been coded to include a link that references customerinformation, that link has typically been placed by hand. If the orderappears elsewhere in the user interface, the link must be hand codedagain. Therefore, if a third party integrates an application to theorder object, the order page will not show that information or providelinks to it, because such links have not been hand coded, even thoughthere may be a link in a representation of the order object that isindependent of the UI.

Further, when applications are developed, objects are commonly defined.Also, objects in the application are captured in an object model of theapplication. However, this information is not used in navigating betweenthe objects.

SUMMARY OF THE INVENTION

A system supplies links between objects. A link service receives ahypermedia link request from a client. The hypermedia link requestidentifies a source object. A link provider analyzes associationmetadata and creates hypermedia links between the source object andassociated objects identified from the metadata.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one embodiment of an object-relational datastorage system.

FIG. 2 is a block diagram of an environment in which the presentinvention can be used.

FIG. 3 is a block diagram of a hypermedia service system in accordancewith one embodiment of the present invention.

FIG. 4 is a flow diagram illustrating how link requests are processed bythe hypermedia service system in accordance with one embodiment of thepresent invention.

FIG. 5 is an illustration of an exemplary user interface.

FIG. 6 is a flow diagram illustrating how links are traversed by thesystem in accordance with one embodiment of the present invention.

FIG. 7 is a flow diagram illustrating how hypermedia providers areregistered in accordance with one embodiment of the present invention.

FIG. 8 shows an association between objects.

FIG. 9 is a block diagram illustrating another embodiment of ahypermedia system.

FIG. 10 is a flow diagram illustrating the operation of the system shownin FIG. 9.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention relates to maintaining links between objects. Inone exemplary embodiment, the links are between objects in anobject-relational (O-R) database, although the objects need not bestored in a database system at all, and the present invention can stillprovide benefits. However, for the sake of the present example, prior todiscussing details of the present invention, an environment in which theinvention may be used will be discussed.

FIG. 1 is a block diagram illustrating one embodiment of a data storageand accessing system 10 in accordance with the present invention. System10 includes data access system (or entity persistence system) 12,relational data store mechanism 14, relational database 16, andclass-table mapping 18. System 10 is illustratively an object-relational(OR) data storage system in which stored data can be referred to interms of entities (or objects) and their properties, rather thanelements of the data base schema, such as tables and columns. FIG. 1illustrates one mechanism for doing this.

As shown in FIG. 1, the data can be organized in terms of entities 20(which is used interchangeably herein with the term objects). Eachentity illustratively includes a metadata portion 22 and a remainingattributes portion 24. The metadata portion 22 describes the entity 20,while the remaining attributes 24 define further attributes of entity20, such as the data stored therein. Each of the attributes in entity 20is mapped to a corresponding entity table 26 and a specific column 28 ina given entity table 26.

Data access system 12 can receive forms of a request such as a query 30which specifies an entity, or portions of an entity or group ofentities, to be retrieved. Query 30 can illustratively be expressed interms of objects (“entities”) and properties rather than in terms oftables and columns. The particular manner in which queries are expresseddoes not form part of the present invention.

Data access system 12 receives the query 30 and accesses class-tablemapping 18. In this way, data access system 12 can determine thelocation of the data for the entities identified by query 30. Dataaccess system 12 includes a translator 13 that translates query 30 intoa relational database query 32 which is suitable for input to relationaldata store mechanism 14. In one illustrative embodiment, relational datastore mechanism 14 is a server that operates according to the SQLprogramming language in accessing relational database 16. Therefore,data access system 12 receives queries 30 in terms of objects andtranslates those queries into an appropriate relational database query32 that is then provided to the data store mechanism (or server) 14which actually accesses the data in relational database 16.

Relational data store mechanism 14 retrieves the requested data andreturns it in the form of relational database results 34. The resultsare returned to data access system 12 which then formulates therelational database results 34 into a requested result set 36. In oneillustrative embodiment, result set 36 is requested in query 30. Query30 may request that the results be output in the form of one or moreobjects or simply as a data set. In any case, data access system 12arranges the relational database results 34 into the proper format andoutputs them as result set 36.

FIG. 2 illustrates an example of a suitable computing system environment100 on which the invention may be implemented. The computing systemenvironment 100 is only one example of a suitable computing environmentand is not intended to suggest any limitation as to the scope of use orfunctionality of the invention. Neither should the computing environment100 be interpreted as having any dependency or requirement relating toany one or combination of components illustrated in the exemplaryoperating environment 100.

The invention is operational with numerous other general purpose orspecial purpose computing system environments or configurations.Examples of well known computing systems, environments, and/orconfigurations that may be suitable for use with the invention include,but are not limited to, personal computers, server computers, hand-heldor laptop devices, multiprocessor systems, microprocessor-based systems,set top boxes, programmable consumer electronics, network PCs,minicomputers, mainframe computers, distributed computing environmentsthat include any of the above systems or devices, and the like.

The invention may be described in the general context ofcomputer-executable instructions, such as program modules, beingexecuted by a computer. Generally, program modules include routines,programs, objects, components, data structures, etc. that performparticular tasks or implement particular abstract data types. Theinvention may also be practiced in distributed computing environmentswhere tasks are performed by remote processing devices that are linkedthrough a communications network. In a distributed computingenvironment, program modules may be located in both local and remotecomputer storage media including memory storage devices.

With reference to FIG. 2, an exemplary system for implementing theinvention includes a general purpose computing device in the form of acomputer 110. Components of computer 110 may include, but are notlimited to, a processing unit 120, a system memory 130, and a system bus121 that couples various system components including the system memoryto the processing unit 120. The system bus 121 may be any of severaltypes of bus structures including a memory bus or memory controller, aperipheral bus, and a local bus using any of a variety of busarchitectures. By way of example, and not limitation, such architecturesinclude Industry Standard Architecture (ISA) bus, Micro ChannelArchitecture (MCA) bus, Enhanced ISA (EISA) bus, Video ElectronicsStandards Association (VESA) local bus, and Peripheral ComponentInterconnect (PCI) bus also known as Mezzanine bus.

Computer 110 typically includes a variety of computer readable media.Computer readable media can be any available media that can be accessedby computer 110 and includes both volatile and nonvolatile media,removable and non-removable media. By way of example, and notlimitation, computer readable media may comprise computer storage mediaand communication media. Computer storage media includes both volatileand nonvolatile, removable and non-removable media implemented in anymethod or technology for storage of information such as computerreadable instructions, data structures, program modules or other data.Computer storage media includes, but is not limited to, RAM, ROM,EEPROM, flash memory or other memory technology, CD-ROM, digitalversatile disks (DVD) or other optical disk storage, magnetic cassettes,magnetic tape, magnetic disk storage or other magnetic storage devices,or any other medium which can be used to store the desired informationand which can be accessed by computer 100. Communication media typicallyembodies computer readable instructions, data structures, programmodules or other data in a modulated data signal such as a carrier WAVor other transport mechanism and includes any information deliverymedia. The term “modulated data signal” means a signal that has one ormore of its characteristics set or changed in such a manner as to encodeinformation in the signal. By way of example, and not limitation,communication media includes wired media such as a wired network ordirect-wired connection, and wireless media such as acoustic, FR,infrared and other wireless media. Combinations of any of the aboveshould also be included within the scope of computer readable media.

The system memory 130 includes computer storage media in the form ofvolatile and/or nonvolatile memory such as read only memory (ROM) 131and random access memory (RAM) 132. A basic input/output system 133(BIOS), containing the basic routines that help to transfer informationbetween elements within computer 110, such as during start-up, istypically stored in ROM 131. RAM 132 typically contains data and/orprogram modules that are immediately accessible to and/or presentlybeing operated on by processing unit 120. By way of example, and notlimitation, FIG. 2 illustrates operating system 134, applicationprograms 135, other program modules 136, and program data 137.

The computer 110 may also include other removable/non-removablevolatile/nonvolatile computer storage media. By way of example only,FIG. 2 illustrates a hard disk drive 141 that reads from or writes tonon-removable, nonvolatile magnetic media, a magnetic disk drive 151that reads from or writes to a removable, nonvolatile magnetic disk 152,and an optical disk drive 155 that reads from or writes to a removable,nonvolatile optical disk 156 such as a CD ROM or other optical media.Other removable/non-removable, volatile/nonvolatile computer storagemedia that can be used in the exemplary operating environment include,but are not limited to, magnetic tape cassettes, flash memory cards,digital versatile disks, digital video tape, solid state RAM, solidstate ROM, and the like. The hard disk drive 141 is typically connectedto the system bus 121 through a non-removable memory interface such asinterface 140, and magnetic disk drive 151 and optical disk drive 155are typically connected to the system bus 121 by a removable memoryinterface, such as interface 150.

The drives and their associated computer storage media discussed aboveand illustrated in FIG. 2, provide storage of computer readableinstructions, data structures, program modules and other data for thecomputer 110. In FIG. 2, for example, hard disk drive 141 is illustratedas storing operating system 144, application programs 145, other programmodules 146, and program data 147. Note that these components can eitherbe the same as or different from operating system 134, applicationprograms 135, other program modules 136, and program data 137. Operatingsystem 144, application programs 145, other program modules 146, andprogram data 147 are given different numbers here to illustrate that, ata minimum, they are different copies.

A user may enter commands and information into the computer 110 throughinput devices such as a keyboard 162, a microphone 163, and a pointingdevice 161, such as a mouse, trackball or touch pad. Other input devices(not shown) may include a joystick, game pad, satellite dish, scanner,or the like. These and other input devices are often connected to theprocessing unit 120 through a user input interface 160 that is coupledto the system bus, but may be connected by other interface and busstructures, such as a parallel port, game port or a universal serial bus(USB). A monitor 191 or other type of display device is also connectedto the system bus 121 via an interface, such as a video interface 190.In addition to the monitor, computers may also include other peripheraloutput devices such as speakers 197 and printer 196, which may beconnected through an output peripheral interface 190.

The computer 110 may operate in a networked environment using logicalconnections to one or more remote computers, such as a remote computer180. The remote computer 180 may be a personal computer, a hand-helddevice, a server, a router, a network PC, a peer device or other commonnetwork node, and typically includes many or all of the elementsdescribed above relative to the computer 110. The logical connectionsdepicted in FIG. 2 include a local area network (LAN) 171 and a widearea network (WAN) 173, but may also include other networks. Suchnetworking environments are commonplace in offices, enterprise-widecomputer networks, intranets and the Internet.

When used in a LAN networking environment, the computer 110 is connectedto the LAN 171 through a network interface or adapter 170. When used ina WAN networking environment, the computer 110 typically includes amodem 172 or other means for establishing communications over the WAN173, such as the Internet. The modem 172, which may be internal orexternal, may be connected to the system bus 121 via the user-inputinterface 160, or other appropriate mechanism. In a networkedenvironment, program modules depicted relative to the computer 110, orportions thereof, may be stored in the remote memory storage device. Byway of example, and not limitation, FIG. 2 illustrates remoteapplication programs 185 as residing on remote computer 180. It will beappreciated that the network connections shown are exemplary and othermeans of establishing a communications link between the computers may beused.

It should be noted that the present invention can be carried out on acomputer system such as that described with respect to FIG. 2. However,the present invention can be carried out on a server, a computer devotedto message handling, or on a distributed system in which differentportions of the present invention are carried out on different parts ofthe distributed computing system.

As stated in the background, conventional user interfaces havetraditionally had any links between objects hand coded. This presents anumber of disadvantages. One aspect of the present invention is a systemfor creating links among objects or entities based on logicalrelationships between those objects, when no physical relationshipnecessarily exists. One embodiment of the invention allows the logicalrelationships among such entities to be surfaced as links in ahyperspace, thus making the entities themselves the nodes of thehyperspace.

In general, “hypermedia” is referred to as a mechanism for navigating ahyperspace which is comprised of a set of nodes and the hypermedia linksthat join those nodes. One embodiment of a hypermedia architecture isillustrated in FIG. 3. The hypermedia architecture 200 shows a client202 that communicates with hypermedia service 204. Hypermedia service204 accesses a provider register 206 and also communicates with a set ofhypermedia providers 208, 210 and 212. Hypermedia service (HMS) 204 isillustratively the central point where clients 202 request hypermedia(i.e., hypermedia links or simply links). Hypermedia providers 208-212are registered with HMS 204. Providers 208-212 are the points at whichthe links are actually created. New providers 208-212 can be registeredwith HMS 204, thus allowing extensibility.

The data that is transferred between client 202 and HMS 204, and betweenHMS 204 and providers 208-212 conforms, in one illustrative embodiment,to an XML schema attached as an exhibit hereto. The definition of a“link” in the schema includes a link category. Link categories arediscussed in greater detail below. Suffice it to say for now that newcategories may be defined by a hypermedia provider, thus allowingadditional extensibility.

FIG. 4 is a flow diagram better illustrating how a client 202 requestslinks from hypermedia system 200, and it will be described inconjunction with FIG. 3. In one embodiment, the HMS 204 and linkproviders 208-212 are objects that expose application programminginterfaces (APIs) having methods to accomplish the functionalitydescribed. The specific details of the API are described in greaterdetail in the appendix hereto. Assume that client 200 is displaying alist of customer entities (where the term “entities” is usedinterchangeably with the term “object”). Assume also that the clientwishes to display a set of links to the user for possible traversal.Client 202 first generates a request for links in terms of a source node(i.e., a source entity or a source object). In this example, the clientwould request the links for the customer object. The request alsoillustratively specifies which categories of links to be retrieved. Thelinks can represent relationships between nodes, as well as actions thatcan be performed on nodes, or any other destinations specified.

There are three types of links that can be retrieved: class links,instance links and instance specific links. Class links have the contextof a class. They represent either a relationship to a destination node,or an action that can be performed. A class link provides informationthat is indicative of where a client can traverse to, or what operationscan be performed, as they pertain to a particular class.

Instance and instance specific links have the context of an instance.The difference between the two types is that instance specific links aredirectly tied to a specific instance of an entity (or object), andinstance links are tied to a class, but an instance of that class mustbe specified in order to traverse the link. An instance or instancespecific link provides information indicative of where the client cantraverse to, and what operations can be performed, with the particularinstance being examined.

All three types of links can be traversed, which is discussed in greaterdetail below with respect to FIG. 6. Traversal returns the destinationnode of the link. If the link represents an action, traversal performsthe action the link represents, and may or may not return a destinationnode.

In accordance with one embodiment of the present invention, the type oflink is not the only manner in which links may be grouped. Links alsoillustratively belong to a link category. One example of a link categoryis a metamodel category. This is described in greater detail below.Briefly, however, links that belong to this link category representassociations between entities. These associations are captured in themetamodel (or object model) of the system.

In addition to being a grouping mechanism, a link category also definesa protocol that is followed by the particular providers 208-212 thatsupplied the link. The link category gives client 202 an indication ofwhat type of information the link represents, and what type of objectwill result from traversal of the link. All links of the same categorycan be handled in the same manner. In this way, client 202 is able todetermine how to handle a link based on the link category to which itbelongs.

Therefore, client 202 may generate the hypermedia request by requestingclass, instance, or instance specific links, or a combination of these.The client 202 can also specify a set of link categories, and only linksfrom those categories will be returned. If no category is specified,links from all categories will be returned. In any case, once client 202has generated the request for links, and identified a node which willserve as the source of the link, it provides the request to HMS 204.Generating the request and providing it to HMS 204 is indicated byblocks 214 and 216 in FIG. 4.

HMS 204 then checks register 206 for information to identify theparticular providers 208-212 that provide links that have, as a sourcenode, the node identified by client 202 as the source of the links. Thisis indicated by block 218. In other words, during the registrationprocess, providers 208-212 provided HMS 204 with information about thelink categories, link types, and node classes for which the providerprovides links. This information is stored in register 206. Therefore,when HMS 204 receives a request from client 202, it checks register 206to determine which providers it should access.

HMS 204 then forwards the request generated by client 202 to theidentified providers 208-212 which will provide links having the sourcenode identified by client 202 as the source of the link. This isindicated by block 220.

The providers which receive the request, in turn, return the requestedlinks to HMS 204. This is indicated by block 222. HMS 204 thenaggregates all of the links from the providers 208-212 which haveresponded with links, and returns those links to client 202. This isindicated by block 224 in FIG. 4.

FIG. 5 shows an exemplary user interface where links have already beenrequested. In FIG. 5, the user interface generator that generatesdisplay 300 is currently rendering a customer list that displaysinformation about a plurality of customer objects 302, 304, 306 and 308.When the user selects a certain customer object, the user interfacegenerates a request requesting links from HMS 204 where the selectedcustomer object 302 is the source link. HMS 204 goes through the processdescribed with respect to FIG. 4 and returns a set of links for whichcustomer entity 302 (which can also be referred to as customer node 302)is the source node. The user interface generating the display can thendisplay the links 310 as desired. In the example shown in FIG. 5, thelinks for which customer node 302 is the source node include an addresslink identifying an Address node associated with customer node 302, anorders link which links to an Orders node corresponding to customer node302 and a general information link which links to a General Informationnode corresponding to customer node 302.

In one example, to traverse one of the links 310, the user simplyselects it (such as by clicking on it with the mouse cursor). FIG. 6 isa flow diagram illustrating what happens when a link is traversed. Afterbeing selected by the user, client 202 sends the link, along with thetraversal request, to HMS 204. This is indicated by block 350 in FIG. 6.The link provided by client 202 is illustratively a class link or aninstance specific link.

HMS 204 then identifies the particular provider 208-212 that providedthe link. This is indicated by block 352. The specific links supplied bythe providers in response to requests is maintained by HMS 204 by addingthis information to the link during the hypermedia request. Thisinformation is then examined during a traversal request. Therefore, HMS204 can identify the provider which supplied the link.

HMS 204 then forwards the traversal request and link to the identifiedprovider. This is indicated by block 354.

The provider traverses the link, returning traversal results to HMS 204.This is indicated by block 356. The traversal results can include adestination node, which is the destination of the link, or performanceof an action represented by the link or both, or other targetsrepresented by the link. For example, if the link represents therelationship between a customer and a query of the customer's orders,traversing the link entails the provider returning the query (which isan entity, like the customer), not the results of executing the query.Likewise, if the link represents the relationship between a customer anda URL of a particular web page containing a map of the customer'saddress, traversing the link returns the URL, it does not open a browserwindow displaying the page pointed to by the URL. In that example, thelink does contain a destination (the URL), but the destination is not anentity or an action. Thus, the traversal result may return an entity,some result which is not an entity, or there may be no substantiveresult returned. If the link represents an action, traversing the linkperforms the action and the result may indicate this. Combinations ofthese types of results can occur as well.

HMS 204, in turn, returns the traversal results to client 202. This isindicated by block 358.

Client 202 illustratively includes a handler that handles the traversalresults. For example, if the traversal returns a query, the clienthandler executes that query against the database and displays theresults to the user. If the query returns a URL, the client handleropens a browser window displaying the page pointed to by the URL, etc.Handling the traversal results at the client is indicated by block 360in FIG. 6.

FIG. 7 is a flow diagram illustrating how a provider is registered withHMS 204. First, HMS 204 receives a request to register a provider. Thisis indicated by block 362.

HMS 204 then checks the security of the requester. This is indicated byblock 364. This involves determining whether the requester hasauthorization to register a provider and can be done in any known way.This is indicated by block 366.

HMS 204 then requests information from the provider about the linkcategories, link types and node classes for which the provider provideslinks. This is indicated by block 368.

The provider returns the information, along with a version identifier.This is indicated by block 370.

HMS 204 then caches the information in provider register 206, andinformation confirming the success of the registration is returned tothe requester. This is indicated by block 372. HMS 204 is then inposition to receive requests for links provided by the newly registeredprovider.

A number of other features of the present invention should be noted. Itcan be seen from the architecture that any number of providers can beadded, at any time. Third party providers who integrate applications tothe entities or objects stored in the database can be added and links tothose third party applications will automatically be returned by HMS204, so long as an appropriate provider is registered with HMS 204.

Also, third parties can define new link categories for which theirproviders will provide links. HMS 204 can operate with no knowledgeabout what the links are, only knowing that the provider will providethose links. The same is true for new links. An existing provider canadd new links and they will be provided when requested. The developerthus need not hand code the links into the system. In one illustrativeembodiment, the providers simply need to implement an interface known toHMS 204, such as those described in the Appendix hereto.

In another illustrative embodiment, the interface implemented by HMS 204derives from the interface implemented by the providers. Therefore, eachHMS 204 can also be a provider and can thus be operably connected toanother HMS 204.

Also, HMS 204 can be implemented both as an XML web service and as aclass which can be called directly if client 202 resides on the sameserver as HMS 204. The providers can also be either deployed remotely asXML web services or on the same server as HMS 204.

It can thus be seen that, in accordance with one embodiment of thepresent invention, the links are requested based on object types (orobject classes) or specific object instances. The presentation of thenodes is decoupled from the nodes themselves. The nodes are instances ofobjects rather than presentation elements, such as web pages. Thisallows client 202 to process or handle the destination node of the linkin any manner it wishes.

FIGS. 8-10 illustrate yet another embodiment of the present invention.In that embodiment, one of providers 208-212 provides links betweenassociated objects based on association metadata. In other words, whendeveloping an application, it is common for a set of objects (such asbusiness objects or entities in a business application) to be defined.Such objects in a business application may include, for example, a“Customer” object, a “SalesPerson” object and an “Order” object. Theseobjects (entities) are interrelated through different associations. Forinstance, an “Order” has both a “Customer” and a “SalesPerson”associated with it. Since these associations exist in the problem domainof the application, they are associations that the end user typicallyunderstands. Therefore, it may be beneficial to allow the end user tonavigate between these associations.

The information that defines these associations is captured in ametamodel (or object model) of the applications as they are beingdeveloped. This information is typically stored as metadata. Forexample, FIG. 8 depicts a relationship between an “Order” entity and a“Customer” entity that is modeled during the application developmentprocess.

There are known tools which can be run against object models generatedduring development of an application. Such tools compile the models intoassociation metadata. In accordance with an illustrative embodiment ofthe invention, this is done and the association metadata is stored.

FIG. 9 is a block diagram of an embodiment of hypermedia system 201 thattakes advantage of the stored association metadata. A number of theitems shown in FIG. 9 are similar to those shown in FIG. 3 and aresimilarly numbered. However, FIG. 9 shows that system 201 also includesa metadata hypermedia provider 400 which is connected to a metadatastore 402.

The metadata associations developed during the application developmentprocess (such as the information shown in FIG. 8 which illustrates anassociation between an “Order” entity and a “Customer” entity) is storedin metadata store 402. FIG. 10 is a flow diagram illustrating theoperation of system 201 in accordance with one embodiment of the presentinvention, and will be described in conjunction with FIG. 9.

It is assumed that metadata hypermedia provider 400 has properlyregistered with HMS 204 and its link and identification data resides inprovider register 206. Client 202 first generates a hypermedia request(or link request) specifying which objects are the source of the linkssought, and which categories of links are to be retrieved. This requestis received by HMS 204. This is indicated by block 404 in FIG. 10. HMS204 then forwards the request on to the appropriate providers, which inthis case will include metadata hypermedia provider 400. This isindicated by block 406.

Provider 400 analyzes association information contained in metadatastore 402. One illustrative design of metadata hypermedia provider 400is discussed in greater detail in the Appendix hereto. Briefly, however,provider 400 examines each association in metadata store 402 which hasbeen requested and determines whether the user has rights to access theassociated entities. Provider 400 can determine whether the user hasrights to access the associated entities by accessing a securitysubsystem, or in any other suitable way. Accessing security does notform part of the present invention. Provider 400 then creates a link foreach association for which the user has access, and places associationinformation in the link. This is indicated by block 408.

Provider 400 identifies (using terminology defined by the UnifiedModeling Language (UML)) simple associations and compositionassociations; these can have a variety of cardinalities, such as 1-1,1-many or many-many relationships. Provider 400 also identifiesinheritance associations. For each association located by provider 400,provider 400 creates a link between the source node and the associatednode. This is indicated by block 410.

The links are returned from provider 400 to HMS 204 as indicated byblock 412, and HMS 204 aggregates all returned links and forwards themon to client 202. This is indicated by block 414. In one embodiment,provider 400 does not return the associated node, but instead returns aquery whose results, if executed, include only the associated node.

By way of example, assume that the source node is a Customer and theassociated node is an Order. For this association, the provider 400 mayreturn a destination object which is the associated Order(s) or even acollection of those Order(s). Alternatively, the destination object is aQuery object which, when executed, returns the Order object(s).

Although the present invention has been described with reference toparticular embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. A system for maintaining hypermedia links between objects, the systemcomprising: a link service receiving a hypermedia request from a client,the hypermedia request identifying a source object; a link providerreceiving an indication of the source object from the link service,analyzing association metadata to identify associated objects associatedwith the source object and creating hypermedia links between the sourceobject and the associated objects the link service further receiving atraversal request identifying a hypermedia link to traverse, andproviding the traversal request to the link provider; and a computerprocessor, being a functional component of the system and activated bythe link service and the link provider to facilitate analyzing theassociation metadata, and identifying a hypermedia link to traverse. 2.The system of claim 1 wherein the link provider is configured to returnthe created hypermedia links to the link service.
 3. The system of claim2 and further comprising: an association metadata store accessible bythe link provider, and storing the association metadata.
 4. The systemof claim 2 wherein the source object is identified as an instance of anobject and wherein the link provider creates hypermedia links betweenthe instance and the associated objects.
 5. The system of claim 2wherein the source object is identified as an object type and whereinthe link provider creates hypermedia links between the object type andassociated objects.
 6. The system of claim 1 wherein the link provideris configured to return a traversal result to the link provider based onthe traversal request.
 7. The system of claim 6 wherein the linkprovider provides the traversal result as a destination object.
 8. Amethod of supplying hypermedia links between objects comprising:registering a link provider with a link service; receiving a linkrequest, at the link service from a client, the link request beingindicative of a source object; accessing a provider with the linkservice to identify one or more link providers that provide links forthe source object; receiving the link request, from the link service, atthe one or more identified link providers; analyzing, at the one or moreidentified link providers, association metadata indicative ofassociations between objects to identify associated objects, associatedwith the source object; creating links at the one or more identifiedlink providers, responsive to the link request, based on the associatedobjects identified providing the created links from the one or moreidentified link providers to the link service.
 9. The method of claim 8,and further comprising: providing the created link from the link serviceto the client.
 10. A computer readable medium storing instructions thatcause a computer to perform the step of: receiving, from a linkprovider, a register request at a link service, the register requestrequesting registration of the link provider with the link service;registering the link provider in a provider register at the linkservice, by querying the link provider for hypermedia links that itprovides; receiving a link request from the link service, the linkrequest identifying a source object; accessing the link register toidentify a link provider that provides links for the source object;providing the link request to the identified link provider, andanalyzing stored association metadata at the identified link provider,based on the link request, to generate hypermedia links between anidentified source object and associated object.
 11. The computerreadable medium of claim 10, wherein analyzing comprises: analyzing theassociation metadata to identify objects associated with the identifiedsource object.
 12. The computer readable medium of claim 11 whereinanalyzing comprises: generating the hypermedia links between theidentified source object and the identified associated objects.
 13. Thecomputer readable medium of claim 10 wherein querying comprises:querying the link provider for categories for which the link providerprovides links.
 14. The computer readable medium of claim 10 whereinquerying comprises: querying the link provider for link types for whichit provides links.
 15. The computer readable medium of claim 10 whereinquerying comprises: querying the link provider for source objects forwhich it provides links.
 16. The computer readable medium for claim 10wherein the associated object is a query object which, when executed,returns other associated objects.